Quick and easy self-rating of Generalized Anxiety Disorder: Validity of the Dutch web-based GAD-7, GAD-2 and GAD-SI
Introduction
DSM-IV Generalized Anxiety Disorder (GAD), with chronic, excessive and uncontrollable worry as central feature (American Psychiatric Association, 1994) is one of the most common of all anxiety disorders (Somers et al., 2006). Estimated lifetime prevalence is 6.2% in the general population (Somers et al., 2006). It is associated with subjective distress due to constant worry and difficulty in controlling worry, resulting in impaired social functioning and quality of life (Hunot, et al., 2007). Several studies have reported effective treatments (both pharmacological and psychological) in reducing GAD-symptoms (Hoffman and Mathew, 2008, Hunot et al., 2007).
Unfortunately, only a minority of anxiety patients are detected in primary care (Kessler et al., 1999). One reason might be that anxiety questionnaires are time consuming and expensive (Zimmerman and Mattia, 2001). The development of brief, patient-completed measures which are easily administered has been stimulated by the need of busy primary care and mental health practitioners (Swinson, 2006) to effectively and feasibly detect GAD (Kroenke et al., 2007). However, there is a paucity of brief, validated and freely available measures for anxiety (Spitzer et al., 2006). To overcome this gap, Spitzer and colleagues developed the 7-item self-rated Generalized Anxiety Disorder Scale (GAD-7; Spitzer et al., 2006). Several studies have reported good psychometric properties for the GAD-7 as well as its two core items (GAD-2) in primary care settings (Kroenke et al., 2007, Spitzer et al., 2006) and in the general population (Lowe et al., 2008). See Supplementary Material 1 for the GAD-7 and GAD-2. Furthermore, both GAD-7 and GAD-2 performed well as screening tools for Panic Disorder, Social Phobia and Post Traumatic Stress Disorder (PTSD [Kroenke et al., 2007]). This finding seems to be in line with a study by Slade and Watson (2006), which concluded that those disorders share a common internalizing factor characterized by an underlying dimension of distress (GAD and PTSD) and fear (Social Phobia and Panic).
Screening via the Internet can be a valid (Buchanan, 2003) and both time and economically efficient tool (Austin et al., 2006). However, the psychometric equivalence between paper-pencil and Internet-versions of the same questionnaire cannot be assumed (Buchanan, 2002, Buchanan, 2003). Several factors might affect the reliability and validity of self-ratings on the Internet. For example, the difference in hardware and software combinations can cause online tests to look different or even to malfunction (Austin et al., 2006, Buchanan and Smith, 1999). Also, the Internet's advantage of greater anonymity might increase honesty and self-disclosure among participants, which too can cause differences in reliability and validity (Joinson, 1999). We therefore investigated whether the psychometric properties of the GAD-7 and GAD-2 paper-pencil version were equivalent to the converted online version. Furthermore, we examined whether the web-based GAD-7 could be further reduced to one item.
This paper aims to validate the Dutch web-based version of the self-rated GAD-7, GAD-2 and a single item from the GAD-7 (GAD-SI). In addition, we investigate its psychometric qualities in screening for Depressive Disorders and three other common anxiety disorders: Panic Disorder, Social Phobia and PTSD.
Section snippets
Subjects and procedure
Data for this paper were collected as part of a larger study of a brief, web-based screener (Web screening questionnaire; WSQ) for common mental disorders (detailed in Donker et al., 2009). In short, participants were recruited from the general population by using Internet banners (Google, Dutch websites on mental health issues). We specifically targeted adults aged 18 or older who were anxious, depressed or drinking too much alcohol — people with a high rate of common mental disorders who are
Demographics
The total sample (N = 502) had a mean age of 43 (S.D. 13, range 18–80); and 285 (57%) of the subjects were female; the majority were Dutch (n = 474; 94%) and 217 (43%) subjects had received medium-level education (Intermediate Vocational Training, school of higher general secondary education or pre-university education). Of the 157 subjects who had completed a CIDI interview, the mean age was 43 (S.D. 15, range 18–80); 89 (57%) were female; the majority were Dutch (n = 146, 94%) and 173 subjects had
Discussion
This study's results suggest that the self-rated web-based Dutch versions of the GAD-7, GAD-SI and GAD-2 are reliable and valid measures to detect GAD. Factor analysis of the GAD-7 confirmed GAD and depression as distinct dimensions, which supports divergent validity and is in line with previous research (Lowe et al., 2008, Spitzer et al., 2006). That the GAD-7 reflects anxiety appropriately is supported by the fact that internal consistency reliability and convergent validity (GAD-7 compared
Acknowledgement
This study is funded by the Faculty of Psychology and Education of the VU University, Amsterdam.
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